Risk factors for cryptorchidism

Abstract

Undescended testis - known as cryptorchidism - is one of the most common congenital abnormalities observed in boys, and is one of the few known risk factors for testicular cancer. The key factors that contribute to the occurrence of cryptorchidism remain elusive. Testicular descent is thought to occur during two hormonally-controlled phases in fetal development - between 8-15 weeks (the first phase of decent) and 25-35 weeks gestation (the second phase of descent); the failure of a testis to descend permanently is probably caused by disruptions to one or both of these phases, but the causes and mechanisms of such disruptions are still unclear. A broad range of putative risk factors have been evaluated in relation to the development of cryptorchidism but their plausibility is still in question. Consistent evidence of an association with cryptorchidism exists for only a few factors, and in those cases in which evidence seems unequivocal the factor is likely to be a surrogate for the true causal exposure. The relative importance of each risk factor could vary considerably between mother-son pairs depending on an array of genetic, maternal, placental and fetal factors - all of which could vary between regions. Thus, the role of causative factors in aetiology of cryptorchidism requires further research.

Figure 1. Descent of the testis

(Modified with permission from Hutson JM, Thorup JM, Beasley SW. Descent of the testis. 2nd ed: Springer, 2016) a) After gestational week 8, the developing testes in males are found lying in an intra-abdominal position. Sometime between the 8^h and 15^th week of gestation, the testes begin the first phase of their descent. b) The second phase of testicular descent (the inguinoscrotal phase) occurs during 25–35 weeks’ gestation. The gubernaculum bulges out from the inguinal region of the abdominal wall and begins to migrate toward the scrotum. c) Around week 35 of gestation, the gubernaculum (with its testis contained inside the processus vaginalis) finally comes to rest in the scrotal sack. d) Once the descent is complete, the processus vaginalis pouch closes at the top of the scrotum. Also at this time, the gubernaculum adheres to the scrotal wall – anchoring both itself and the contained testis into their terminal position – while the remnants of the processus vaginalis above the scrotum regress.